The invention relates to a process for preparing polyfluoroalkyl-lithium compounds by deprotonation of polyfluoroalkyl compounds by means of lithium bases.
Organic compounds that are substituted by polyfluoroalkyl groups are becoming increasingly important, for example, in the development of new active compounds, since such substituents are inert under physiological conditions and allow fine control of, for example, the lipophilicity and the reactivity of the basic organic skeleton.
The introduction of polyfluoroalkyl substituents into an organic molecule is frequently carried out using polyfluoroalkyl-metal compounds that can undergo the addition and substitution reactions typical of nucleophilic reagents.
Thus, for example, the synthesis of pentafluoroethyltrimethylsilane, a reagent for the preparation of pentafluoroethylated products, can be carried out by reaction of pentafluoroethyllithium (for the preparation of which, see, for example, P. G. Gassmann and N. J. O'Reilly, Tetrahedron 1985, 26, page 5243) with trimethylchlorosilane according to equation (a).CF3CF2Li+(CH3)3SiCl→(CH3)3SiCF2CF3+LiCl  (a)
In addition, such organometallic compounds react with aldehydes, as shown in equation (b), to form polyfluoroalkyl-substituted alcohols that are valuable starting materials for the production of materials for liquid crystal displays (LCDs) and are therefore of industrial interest. 
The polyfluoroalkyl compounds of the metals magnesium and zinc have also been examined (R. D. Chambers, W. K. R. Musgrave, and J. Savory, J. Chem. Soc., 1962, pages 1993-1999). However, compared with their lithium analogs, these compounds display only unsatisfactory reactivity, so that they do not come into question for industrial use.
In the past, polyfluoroalkyllithium compounds (RF—Li) have been obtained exclusively by means of metal-halogen exchange reactions according to equation (c), with the replaceable halogens of the starting compounds being able to be chlorine, bromine or iodine.R—Li+RF—Hal→R—Hal+RF—Li  (c)
Recently, however, chlorofluorocarbons (CFCs) in particular have been the subject of replacement measures because of the damage they cause to the ozone layer. The likewise ozone-depleting bromine and iodine homologs have the additional disadvantage that they are not only very expensive but, due to their high molar mass, their use results in formation of large amounts of waste products for which correct disposal represents an additional problem.
There is therefore a need to prepare the synthetic valuable poly-fluoroalkyllithium compounds without use of mixed halofluorocarbons.
It has now been found that polyfluoroalkyl compounds can be deprotonated by means of lithium bases.